Aqueous solution and method for use thereof

Abstract

A method of treating a formation includes preparing an aqueous solution having HCl in an amount between greater than 15% and 45.7% by weight, inclusive. The prepared aqueous solution includes a fixing agent (FA) present in a molar ratio of FA:HCl between 0.15 and 2.5 inclusive, where the FA is urea and/or a urea derivative, and further includes water present in an amount sufficient to dissolve the HCl and the FA. The aqueous solution includes substantially no polysaccharides. The method further includes providing an oilfield treatment fluid including the aqueous solution to a high pressure pump operating the high pressure pump to treat a wellbore and/or the formation fluidly coupled to the wellbore.

We claim: 
     
         1 . An aqueous solution, comprising:
 HCl in an amount between a first value exceeding 15% and a second value of 45.7% by weight, inclusive;   a fixing agent (FA) present in a molar ratio of FA:HCl between 0.15 and 2.5 inclusive, wherein the FA comprises at least one of urea and a urea derivative;   water present in an amount sufficient to dissolve the HCl and the FA; and   wherein the aqueous solution comprises substantially no polysaccharides.   
     
     
         2 . The aqueous solution of  claim 1 , wherein the FA is further present in a molar ratio of FA:HCl having one of the range values selected from the range values consisting of: between 1.0 and 2.0 inclusive, between 0.5 and 2.0 inclusive, between 0.5 and 1.25 inclusive, between 0.3 and 1.25 inclusive, between 1.0 and 1.7 inclusive, and about 1.7. 
     
     
         3 . The aqueous solution of  claim 1 , further comprising HF in an amount of at least 0.25% by weight. 
     
     
         4 . The aqueous solution of  claim 1 , wherein the FA further comprises at least one molecular species, and wherein the aqueous solution further comprises a formulation selected from the formulations consisting of:
 each of the at least one molecular species comprising a molecule having a molecular weight below 100 g/mol, and wherein the FA is further present in a molar ratio of FA:HCl between 0.3 and 1.65 inclusive;   each of the at least one molecular species comprising a molecule having a molecular weight below 120 g/mol, and wherein the FA is further present in a molar ratio of FA:HCl between 0.27 and 1.25 inclusive;   each of the at least one molecular species comprising a molecule having a molecular weight below 150 g/mol, and wherein the FA is further present in a molar ratio of FA:HCl between 0.22 and 1.05 inclusive; and   each of the at least one molecular species comprising a molecule having a molecular weight below 175 g/mol, and wherein the FA is further present in a molar ratio of FA:HCl between 0.18 and 1.0 inclusive.   
     
     
         5 . The aqueous solution of  claim 1 , wherein the FA comprises urea, and wherein the FA is further present in a molar ratio of FA:HCl between 0.5 and 2.25 inclusive. 
     
     
         6 . The aqueous solution of  claim 1 , wherein the aqueous solution does not include a separate acid retarder, and wherein the aqueous solution exhibits an acid retardation factor of at least 3 at 20° C. (68° F.). 
     
     
         7 . The aqueous solution of  claim 1 , wherein the aqueous solution does not include a separate acid retarder, and wherein the aqueous solution exhibits an acid retardation factor of at least 10 at 20° C. (68° F.). 
     
     
         8 . A method of treating a formation, comprising:
 preparing an aqueous solution comprising HCl in an amount between a first value exceeding 15% and second value of 45.7% by weight, inclusive, a fixing agent (FA) present in a molar ratio of FA:HCl between 0.15 and 2.5 inclusive, wherein the FA comprises at least one of urea and a urea derivative, water present in an amount sufficient to dissolve the HCl and the FA, and wherein the aqueous solution comprises substantially no polysaccharides;   providing an oilfield treatment fluid including the aqueous solution to a high pressure pump; and   operating the high pressure pump to treat at least one of a wellbore and the formation fluidly coupled to the wellbore.   
     
     
         9 . The method of  claim 8 , wherein the providing the oilfield treatment fluid further comprises diluting the aqueous solution to an HCl amount of not greater than 28% by weight inclusive. 
     
     
         10 . The method of  claim 9 , wherein the aqueous solution further comprises an HCl amount between the first value exceeding 37% and the second value of 45.7%, the method further including transporting the aqueous solution to a location in treatment proximity to the wellbore, and wherein the providing the oilfield treatment fluid further comprises diluting the aqueous solution to a treatment concentration before the providing the oilfield treatment fluid to the high pressure pump. 
     
     
         11 . The method of  claim 10 , wherein the preparing the aqueous solution further comprises preparing the aqueous solution without a separate acid retarder, and preparing the aqueous solution to exhibit an acid retardation factor at 20° C. (68° F.) selected from the acid retardation factors consisting of: at least 3, at least 8, at least 10, at least 12, at least 14, and at least 20. 
     
     
         12 . The method of  claim 10 , wherein the diluting further comprises adding an additional amount of the FA, and wherein the FA is further present in the oilfield treatment fluid in a molar ratio of FA:HCl between 1 and 2 inclusive. 
     
     
         13 . The method of  claim 12 , wherein operating the pump comprises at least one of:
 injecting the oilfield treatment fluid into the formation at matrix rates;   injecting the oilfield treatment fluid into the formation at a pressure at least equal to the hydraulic fracturing pressure; and   contacting at least one of the wellbore and the formation with the oilfield treatment fluid.   
     
     
         14 . The method of  claim 8 , wherein the oilfield treatment fluid further includes HF in an amount of at least 0.25%. 
     
     
         15 . The method of  claim 8 , wherein the formation comprises a temperature of greater than 225° F. (107° C.). 
     
     
         16 . The method of  claim 15 , wherein the oilfield treatment fluid does not include a separate acid retarder. 
     
     
         17 . The method of  claim 16 , wherein the formation comprises a temperature between 300° F. (149° C.) and 350° F. (177° C.), and wherein the oilfield treatment fluid further includes the urea in a molar ratio of urea:HCl between 1.5 and 2 inclusive. 
     
     
         18 . A method, comprising:
 preparing a first aqueous solution comprising HCl in an amount between 7.5% and 37% by weight, inclusive;   preparing a second aqueous solution comprising at least one of urea and a urea derivative in an amount of at least 10% by weight and 55% by weight, inclusive;   treating a formation fluidly coupled to a wellbore with a first oilfield treatment fluid including the first aqueous solution and with a second oilfield treatment fluid including the second aqueous solution; and   wherein the treating is performed sequentially and with either the first oilfield treatment fluid or the second oilfield treatment fluid being first.   
     
     
         19 . The method of  claim 18 , wherein the first aqueous solution further comprises a fixing agent (FA) present in a molar ratio of FA:HCl between 0.15 and 2.5 inclusive, wherein the FA comprises at least one of urea and a urea derivative. 
     
     
         20 . The method of  claim 18 , wherein the second aqueous solution further comprises HCl in an amount between a first value exceeding 15% and a second value of 28% by weight, inclusive, wherein the at least one of urea and a urea derivative comprises a fixing agent (FA) which is further present in a molar ratio of FA:HCl between 0.15 and 2.5 inclusive, and wherein the second aqueous solution further comprises substantially no polysaccharides.